This invention relates generally to furnaces and, more particularly, to a method and apparatus for attaching an air baffle to a furnace heat exchanger.
Residential furnaces typically include a plurality of heat exchanger panels or cells arranged in parallel relationship, with the air to be heated being circulated by a blower so as to pass between the panels and over the surfaces of the panels to be heated. The panels have associated burners for heating the air within the panels, and an inducer may be employed to draw the heated air through the panels and discharge them to a flue.
In order to improve the heat transfer efficiency of the furnace heat exchangers and maintain a more uniform distribution of temperatures across the surfaces of the heat exchangers, it has become common practice to use baffles to selectively channel the flow of circulating air over the heat exchanger surfaces. For example, a blower shelf baffle has been provided to turn a horizontal component of the circulating air coming off the fan to flow in a more vertical upward direction. Also, sidewall baffles have been used to break up the laminar flow along the sidewalls and redirect it outwardly toward the heat exchangers. Similarly, a rear wall baffle has been used for diverting the flow of air away from the rear wall and outwardly toward the heat exchanger panels. In each case, it has generally been the practice to attach these baffles to the furnace casing or to the blower shelf by fasteners or the like.
While the rear wall baffle may comprise a single element extending continuously across the rear wall so as to uniformly channel the airflow outwardly, it preferably includes a plurality of baffle elements that are selectively spaced across the rear wall in relation to the spacing of the heat exchanger panels. That is, the baffles extend outwardly beyond the rear edges of the heat exchanger panel structures so as to collectively wrap around those edges to more effectively channel the airflow as desired. With this feature, the baffles can also serve a second function of maintaining proper spacing between panels by engaging the edges of the panels on either side thereof. However, if the heat exchanger panels move with respect to the rear wall, as tends to occur because of the significant volume of circulating air flowing thereover, then the movement between the baffles and the panels will cause undesired noise and possible misalignment.
One form of heat exchanger that is commonly used in such furnaces is a so-called clamshell heat exchanger, wherein two stamped metal shells are fastened together to form a single panel having a plurality of serpentine passages, or passes, through which the hot gases can be caused to flow. Thus, the panels are generally rectangular in form, and have a border and portions between the passages which are planar in form and made up of two thicknesses of sheet metal pressed together. These portions can be referred to as lands. Since the lands are not part of the structure which carries the hot gases, they are available for purposes of attaching a baffle to the panels. However, it is difficult to attach a fastener that extends normally through the lands at the border portion of the panel because of the limited distance between adjacent panels. And, heretofore, there has been no way to attach a fastener that extends in the plane of the respective panels
In a serpentine, clamshell exchanger panel, a burner heats the air at an inlet end thereof, and the hot gases pass through successive passes and finally come out of the exit end of the panel to eventually be discharged to the flu. As the gases pass from the inlet to the exit end of the panel, they are cooled by the air being circulated over the surface of the panel. Thus, the gases in the first pass are at substantially higher temperatures than those downstream thereof, and care must be taken to prevent the occurrence of excessive temperatures. In particular, hot spots are most likely to occur in the vicinity between the first return bend and the second pass. These hot spots cause exposure to high temperatures that can cause excessive strain levels in the material of the heat exchanger structure and may eventually lead to failure.
It is therefore an object of the present invention to provide an improved method and apparatus for mounting a rear wall baffle in a furnace. This object and other features and advantages become more readily apparent upon reference to the following descriptions when taken in conjunction with the appended drawings.